IFR Technique: Glass-panel precision

Sure, the approach procedures, navigational fixes, glideslope intercept points, needle sensitivity, and minimum descent altitudes are identical, and air traffic controllers rightly treat glass panel and analog airplanes just the same. For pilots, however, IFR techniques—and the flying skills required—are strikingly dissimilar when operating glass-panel avionics compared to analog gauges.

Consider a plain-vanilla ILS approach flown in a Beechcraft Bonanza A36 with a traditional six-pack panel, for example. The pilot’s eyes shift to and from the attitude indicator during a ceaseless scan, and the pilot assembles a comprehensive mental picture of the aircraft’s changing status as it approaches an airport for landing.

The pilot analytically determines the airplane’s attitude, airspeed, power setting, position, height above the ground, configuration, and energy state from this series of mental snapshots. Cross-referencing primary and supporting instruments allows the pilot to keep the airplane properly oriented through a series of configuration changes during descent and landing. It’s a nonstop aviation version of the childhood game: “What’s wrong with this picture?”

Along the way, pilots monitor their progress on approach plates that allow verification of their current position and anticipation of next steps. Power settings are predetermined from previous experience (and the old truism “pitch plus power equals performance”). The ballpark power settings are close enough to ensure the airplane is below landing gear and flap deployment speeds along the way. (In this case, about 18 inches of manifold pressure and approach flaps in level flight, then lower the landing gear one dot below glideslope intercept to establish a roughly 500-foot-per-minute descent.)

Control inputs are intentionally mechanical. The pilot brackets the localizer by tapping the rudder pedals. At the same time, the pilot tracks the ILS glideslope by moving the yoke fore and aft, then adjusting elevator trim. Airspeed adjustments are made with power.

The heading bug on the directional gyro is set to the localizer course, and the pilot notes the amount of crosswind correction needed to keep the increasingly sensitive horizontal situation indicator (HSI) needles centered throughout the descent.

The pilot keeps decision height firmly in mind as the airplane nears that hard number at which the runway environment must be visible, or the missed approach must begin.

A video game

Now, consider the same ILS approach in the same model airplane with a modern glass panel that includes primary and multi-function displays.

The first and biggest difference to the pilot is that the instrument scan is replaced with the instrument stare. All the relevant information about the airplane’s attitude, airspeed, altitude, power setting, and position relative to the airport are shown on the primary flight display. GPS-derived synthetic vision gives a broad, colorful view of the landscape and terrain features ahead, and the act of flying the airplane is much the same as it is in visual conditions.

A series of rectangular highway-in-the-sky boxes graphically depict the path for the airplane to follow during the approach. Those boxes follow the 3-degree ILS glideslope and localizer all the way from glideslope intercept down to the runway threshold.

Instead of dividing attention between multiple analog instruments, the pilot focuses on placing the green dot/flightpath marker in the center of the boxes and keeping it there. There’s no need to build a mental picture of the airplane’s position, attitude, and energy state because that information is constantly depicted with high-resolution graphics. The act of flying the airplane during the approach is no longer an abstract analytical exercise—it’s a video game.

Instead of crunching numbers and comparing them to the ones found on the approach plate, the glass-panel pilot monitors the airplane’s progress by glancing at the georeferenced approach procedure on the multifunction display. The airplane is graphically shown in real time on the approach plate itself, so there’s no real interpretation for the pilot to do. The pilot simply takes note of the current situation and considers what’s going to happen next.

When the GPS-derived synthetic vision image of the landing runway appears on the primary flight display (usually about four miles out), the pilot adjusts the flight controls to place the flightpath marker on the threshold. Using coordinated control inputs, the pilot smoothly adjusts pitch and power together, just the same as they would during a visual approach. Nearing decision height, the glass-panel pilot gets an aural cue when the airplane is 500 feet above the ground, and another at decision height when an automated voice calls out “minimums.” Here, just as with analog gauges, the pilot must either see the runway environment or begin the missed approach.

A missed approach with an analog panel can be a stressful, confusing, high-workload event. The pilot must add power, configure the airplane, climb to a heading and altitude (or series of headings and altitudes), and tune, identify, and track new navigation sources. That can mean changing modes in a GPS navigator or switching nav radio frequencies and/or VOR radials.

Published missed approach procedures typically include a hold, and once there, the pilot determines whether to set up for another approach or divert to an alternate airport. That means getting updated weather information and evaluating fuel quantity, wind, range, and more.

A missed approach in a glass-panel airplane is far simpler. The pilot begins a climb, configures the airplane, and follows the highway-in-the-sky and moving-map guidance to the holding fix. Once there, the boxes show the proper, wind-corrected path to follow throughout the hold. A quick look at the multifunction display shows a graphical depiction of the current weather, and the pilot can tell at a glance from color-coded airport flags how far they must fly for improved weather conditions.

Some GPS navigators such as the Garmin GNS 650/750 require the pilot to “suspend” an approach to begin the missed approach. Others such as the Avidyne IFD series do it automatically.

Where to look

Analog avionics require pilots to scan, correctly interpret, and compare information from multiple instruments, build accurate mental pictures of the dynamic situation around them, and fly with self-discipline and precision. Those are hard-won skills that require repetition and vigilance under normal conditions—and they become especially demanding during abnormal situations such as vacuum-system failures that create “partial-panel” conditions. There’s a right way to perform each task, a correct sequence for doing them, and a high price to pay for mistakes.

Digital, glass-panel avionics are inherently more reliable, provide greater redundancy, and there is surprising flexibility in the ways that pilots can employ them. Pilots can customize how they choose to display information, and what they want to prioritize during each phase of flight.

For example, there’s technically no right or wrong way to configure a moving map (north up or track up?) although individual pilots have strong preferences (track up!). Or whether to split panels or show geo-referenced approach plates while flying them.

If pilots want to focus on the flight director during an approach, they can. If they prefer to emphasize the flightpath marker, they can follow it instead. The tyranny of HSI needles is over because that formerly all-important instrument has been demoted to a supporting role.

No matter how pilots set up and fly glass panels, however, the skills and mindset they require are different than the ones instrument pilots have traditionally practiced.

Fortunately, the new technology can provide better situational awareness than pilots have ever had, enhance safety, and allow us to fly more smoothly and with greater precision than ever.

We’ve just got to know where to look.  

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